A busy railway station concourse seen from above, with travellers walking in soft focus
AI-generated image, not a photograph of a real person or place.
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WHAT THE RESEARCH SAYS

Friends at a glance,
strangers by guesswork.

5,000 faces known, on average

  • Familiar faces are easy
  • Unfamiliar faces are hard
  • One photo is not enough
  • Familiarity is everything

You can spot a friend across a crowded room in an instant.

Researchers at the University of York estimated that people know about 5,000 faces. But faces we do not know are another matter: matching a stranger to their photo is hard, and training and experience do not seem to fix it.

Updated

Test your intuition

THE SHORT ANSWER

We know thousands,
but only the ones we know.

Face recognition is really two skills.
One works brilliantly for familiar people. The other, for strangers, is shaky.

FAMILIAR FACES

About 5,000 faces

Participants in a York study knew between 1,000 and 10,000 faces, about 5,000 on average, from their own lives and the media.

See the numbers

SAME PERSON, NEW PHOTO

Strangers split in two

Shown many photos of one unfamiliar person, viewers often decide they are several different people. People who know the face sort the same photos perfectly.

Why photos vary

PHOTO ID

Experts struggle too

Passport officers checking people against photos accepted 14% of fraudulent photos, and did no better than students.

Test your intuition

A QUICK FACE CHECK

How reliable is
this face judgement?

Pick a situation. The bar shows how error-prone the research found it to be.

Face check

Choose a situation
Recognising a friend in a photo you have never seenNear perfect

In Jenkins and colleagues' sorting study, people familiar with the faces identified the same varied photos perfectly.

Deciding if two photos of strangers show the same person≈ 81% correct

On the Glasgow Face Matching Test, a standard task where guessing scores 50%, the normal average is 81.3%.

Checking a stranger against their photo ID14% of fakes passed

Passport officers made an average of 10% errors comparing people to photos, wrongly accepting 14% of fraudulent photos.

Sorting many photos of two strangersMedian 5 'people'

Adults given 40 photos of two unfamiliar men split them into a median of 5 identities, ranging from 2 to 28.

A checker with years of experienceNo better

Length of employment did not predict passport officers' accuracy, though some individuals were very accurate.

Sources: White and colleagues, Passport officers' errors in face matching (PLOS ONE, 2014); Jenkins and colleagues, Variability in photos of the same face (Cognition, 2011); Neil and colleagues (Journal of Experimental Child Psychology, 2016).

Based on peer-reviewed studies of face matching and face sorting (2011 to 2016).

TWO NUMBERS WORTH KNOWING

Thousands known,
fakes still missed.

One figure on how many faces we carry,
one on how often trained staff miss a fake.

≈ 5,000

Average number of faces a person knows

Participants spent an hour listing faces from their personal lives, then famous faces, and were tested on thousands of photos of famous people. They knew between 1,000 and 10,000 faces. Their mean age was 24.

FACES KNOWN · UNIVERSITY OF YORK

14%

Fraudulent photos accepted by passport officers

Thirty passport officers compared live people with photo IDs. They made 10% errors on average, rejecting 6% of valid photos and accepting 14% of fraudulent ones.

PHOTO ID · PLOS ONE, 2014

The York researchers point out that humans typically lived in small groups of around one hundred people, yet we handle thousands of faces. Dr Rob Jenkins said they had not yet found a limit on how many faces the brain can handle.

FOUR THINGS TO TAKE AWAY

Trust familiarity,
doubt the snapshot.

A hand holding a plain identity card with a blank photo panel at a desk, seen from behind
AI-generated image, not a photograph of a real person or place.

The research has practical lessons for anyone who has ever waved at a stranger or puzzled over an old photo.

  1. Familiar beats expert

    Knowing someone helps more than training: familiar viewers sorted varied photos perfectly, while experienced passport officers matched strangers no better than students.

  2. One photo is a poor likeness

    Photos of the same person form a range from good to bad likeness. Jenkins and colleagues concluded that face photographs are unsuitable as proof of identity.

  3. Knowing it is one person helps

    Viewers told that only two people were in a set of photos later matched those faces more accurately than people who sorted with no hint.

  4. Skill varies widely

    Some people match unfamiliar faces with 100% accuracy and others fall below 70%. The PLOS ONE authors suggest selecting staff for aptitude.

WHY PHOTOS VARY

One face,
many looks.

Hands spreading a set of printed portrait photos across a table, the faces turned away or blurred
AI-generated image, not a photograph of a real person or place.

Lighting, angle, age and expression change how a face looks in a photo. Jenkins and colleagues found that this within-person variability is often very large compared with the differences between people.

Familiarity seems to work by learning that range. In one study, people sorting photos of two unfamiliar faces with no hint made 7.5 piles on average; those told there were two did better on a later matching test.

Questions

Questions people ask

How many faces does the average person know?

A University of York study estimated about 5,000 on average, with participants knowing between 1,000 and 10,000 faces.

Why is it hard to match a stranger to a photo?

Photos of the same person vary a lot with lighting, angle and age. Without knowing the face, viewers often see different photos of one person as different people.

Are passport officers better at matching faces?

Not on average. In a 2014 PLOS ONE study, passport officers did no better than students, and their accuracy was not linked to how long they had been in the job.

Does everyone find unfamiliar faces equally hard?

No. Researchers found very large individual differences: some people scored 100% on face matching tasks while others fell below 70%, where guessing gives 50%.

Is there a limit on how many faces we can know?

The York team said they had not yet found a limit on how many faces the brain can handle.

Sources

Where the facts come from

  1. University of York: Never forget a face? Research suggests people know an average of 5,000 faces (2018)
  2. White, Kemp, Jenkins, Matheson and Burton, Passport officers' errors in face matching, PLOS ONE (2014)
  3. Jenkins, White, Van Montfort and Burton, Variability in photos of the same face, Cognition (2011), University of Glasgow repository
  4. Neil and colleagues, Recognizing the same face in different contexts, Journal of Experimental Child Psychology (2016), PMC
  5. The role of within-person variability in forming stable face representations, PMC

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